[0001] The present invention relates to a method for the fractionation of sulphite cooking
liquor by a chromatographic simulated moving bed system in which the liquid flow is
effected in a system comprising at least two chromatographic sectional packing material
beds. By the method of the invention, sulphite cooking liquor can be fractionated
to yield at least two fractions. The invention is related in particular to fractionation
of sulphite cooking liquor into at least three fractions, xylose being concentrated
in one of said fractions and lignosulphonates being concentrated in another of said
fractions. The invention offers an advantageous method particularly for the recovery
of xylose from hardwood sulphite cooking liquor in a continuous process. Typically
in this method lignosulphonates are recovered as the most rapidly eluted product fraction,
and xylose which is the slowest to elute is recovered as the third product fraction.
[0002] By sulphite cooking liquor in this context is meant liquor employed in the cooking
of sulphite cellulose, liquor ensuing from the cooking, or a part thereof.
[0003] In the method of the invention, the product or products are recovered using a multi-step
sequence comprising the following phases: feeding phase of sulphite cooking liquor,
eluting phase and recycling phase.
[0004] In the feeding phase sulphite cooking liquor is introduced into the sectional packing
material bed and simultaneously a corresponding amount of product fraction is withdrawn
from a later point downstream in the same sectional packing material bed or from a
downstream sectional packing material bed (possibly through one or more other sectional
packing material beds) connected in series with said bed. The feeding phase may also
include all sectional packing material beds in the system.
[0005] In the recycling phase the liquid present in the sectional packing material beds
with its dry solids profile is recycled in a loop comprising one, two or several sectional
packing material beds; this may also include all sectional packing material beds in
the system.
[0006] The eluting phase comprises feeding of an eluent into a sectional packing material
bed and respectively withdrawal of a product fraction or fractions from a downstream
point of the packing material bed, from the same sectional packing material bed or
a downstream sectional packing material bed.
[0007] A process step comprises one or more of the above simultaneous identical or different
phases. A step can consist of, for example, a mere feeding phase, recycling phase
or eluting phase, a feeding phase and (a) simultaneous recycling and/or eluting phase(s),
an eluting phase and (a) simultaneous recycling phase(s), a recycling phase and (a)
simultaneous eluting phase(s) etc., and said steps are repeated from one to five times
during the sequence.
[0008] Said phases are employed to form sequences comprising several successive process
steps. In accordance with the invention, a sequence preferably comprises four to ten
steps.
[0009] A sequence comprising said steps is repeated five to seven times to equilibrate the
system, whereafter the process is continued in a state of equilibrium.
[0010] Typically from two to twelve, preferably two to six, chromatographic sectional packing
material beds combined into one or more loops are employed in the method of the invention.
A loop may comprise one, two or several sectional packing material beds packed into
one or more columns.
[0011] The sulphite cooking liquor comprises, in addition to the cooking chemicals, for
example undissolved wood material, lignosulphonates, organic acids, hexose and pentose
sugars derived as hydrolysis products of hemicellulose, and also small amounts of
oligosaccharides if hydrolysis into monosaccharides has been incomplete. Normally
a low pH in pulp cooking contributes to the hydrolysis of hemicellulose into monosaccharides.
When the pulp is produced from hardwood, the major part of the monosaccharides contained
in the cooking liquor consists of xylose, which can be employed as a raw material
in the production of crystalline xylose, xylitol and furfural, for instance. When
pulp is produced from softwood, the prevalent monosaccharide in the cooking liquor
is mannose.
[0012] Economical use of sulphite cooking liquor requires that it is fractionated into its
constituents. Fractionating methods suitable for this purpose are disclosed in U.S.
Patent 4 631 129 and the references incorporated therein. In accordance with U.S.
Patent 4 631 129, the sugars and lignosulphonates can be separated from sulphite spent
liquor by a method comprising two chromatographic treatments: in the first treatment,
sulphite spent liquor is introduced into a chromatographic column which comprises
a strongly acid resin in salt form employed as the column packing material and from
which a substantially sugarless fraction rich in lignosulphonates and a fraction rich
in sugars are obtained by elution; in the second chromatographic treatment, said fraction
which is rich in sugars and the pH of which has been adjusted to 5.5-6.5 is introduced
into a second chromatographic column comprising resin in monovalent salt form, and
elution thereof yields a second fraction rich in sugars and a second fraction containing
lignosulphonates and salts. The method is stated to achieve recovery of sugars, e.g.
xylose contained in hardwood sulphite spent liquor, in high purity and high yields.
However, the fractionating methods for sulphite cooking liquor in accordance with
U.S. Patent 4 631 129 and other prior art are attended by the drawback that they are
typically batch methods and are not advantageous in large-scale fractionation of cooking
liquor.
[0013] Methods are also known for fractionating sulphite cooking liquor by ultrafiltration
[cf. e.g. Trivedi, M. K., Fung, D. P. C. and Shen, K. C., Tappi
61 (1978) No. 11, pp. 119-120]. By these methods, which yield only two product fractions,
large-molecule lignosulphonates can be recovered; the sugars however end up in the
same fraction with the salts.
[0014] U.S. Patents 4 008 285 and 4 075 406 teach recovery of xylose by a chromatographic
method. In this method, a pentosan-containing biomass, e.g. wood raw material, is
hydrolysed, the hydrolysate is purified by ion exclusion and colour removal and the
resultant solution is fractionated chromatographically to obtain a solution rich in
xylose. The fractionating methods disclosed in these patents are also batch processes,
and only two product fractions are disclosed to be obtained thereby.
[0015] DE Patent 1 692 889 discloses recovery of xylose from sulphite spent liquor by a
method in which the spent liquor is extracted with aliphatic alcohols containing 1-5
carbon atoms, the water and alcohol layers formed are separated, alcohol is removed
from the latter by distillation, and the resultant syrup-like residue in which the
ratio of xylose to lignosulphonates is at most 1:2.5, is maintained at a temperature
below room temperature until the xylose is crystallized. The crystallized xylose is
ground with ethanol, filtered, and dried. In this method, the lignosulphonates remain
in the mother liquor with the salts.
[0016] It is an object of the present invention to provide a chromatographic method for
continuous fractionation of sulphite cooking liquor, in particular for continuous
fractionation of hardwood sulphite cooking liquor, enabling recovery of xylose and
lignosulphonates from the cooking liquor.
[0017] Continuous chromatographic separation processes have in recent years employed what
is known as the simulated moving bed system. It was developed and introduced in the
U.S.A. at the beginning of the 1960s, initially for petrochemical applications (U.S.
Patent 2 985 589). Today several simulated moving bed methods for a number of different
applications are known (U.S. Patents 3 706 812, 4 157 267, 4 267 054, 4 293 346, 4
312 678, 4 313 015, 4 332 623, 4 359 430, 4 379 751, 4 402 832, 4 412 866, 4 461 649,
4 533 398 and 5 127 957, and published European application 0 279 946).
[0018] The simulated moving bed method enables separating performances that are many times
higher, and also considerably lower dilution of the products (consumption of eluent),
than the batch method.
[0019] The simulated moving bed method may be either continuous or sequential.
[0020] In a continuous simulated moving bed method, typically all flows are continuous.
These flows are: supply of feed solution and eluent, recycling of liquid mixture and
withdrawal of products (usually only two). The flow rate for these flows may be adjusted
in accordance with the separation goals (yield, purity, capacity). Normally, 8 to
20 sectional packing material beds are combined into a single loop. In accordance
with the above-mentioned U.S. Patent 4 402 832, the recycling phases have been employed
in recycling dilute fractions. The feed and product withdrawal points are shifted
cyclically in the downstream direction in the packing material bed. On account of
the supply of eluent and feed solution (and on account of withdrawal of products)
and the flow through the packing material bed, a dry solids profile is formed in the
packing material bed. Constituents having a lower migration rate in the packing bed
are concentrated at the back slope of the dry solids profile, and respectively ingredients
having a higher migration rate at the front slope. The feed points for feed solution
and eluent and withdrawal points for the product or products are shifted gradually
at substantially the same rate at which the dry solids profile moves in the packing
material bed. The product or products are withdrawn substantially from the front and
back slopes of the dry solids profile; the feed solution is introduced approximately
to the maximum point of the dry solids profile and the eluent approximately to the
minimum point of the dry solids profile. Part of the separated products are recycled
on account of the continuous cyclic flow, and only part of the dry solids profile
is withdrawn from the packing material bed during one sequence.
[0021] The feed and withdrawal points are shifted cyclically by using feed and product valves
and feeding and collection devices located along the packing material bed typically
at the upstream and downstream end of each packing material bed. If it is desired
to recover product fractions of high purity, short phase times and a plurality of
sectional packing material beds must be employed (the apparatus has corresponding
valves and feed and withdrawal equipment).
[0022] In a sequential simulated moving bed system, not all flows are continuous. In a sequential
simulated moving bed method the flows are: supply of feed solution and eluent, recycling
of liquid mixture and withdrawal of products (eluting step; two to four, or more,
products). The flow rate and the volumes of the different feeds and product fractions
may be adjusted in accordance with the separation goals (yield, purity, capacity).
The method comprises three basic phases: feed, elution, and recycling. During the
feeding phase, a feed solution, and possibly also an eluent during a simultaneous
eluting phase, is introduced into predetermined sectional packing material beds, and
simultaneously two, three or even four product fractions are withdrawn. During the
eluting phase, eluent is introduced into a predetermined sectional packing material
bed or predetermined sectional packing material beds, and during said phases two,
three or even four product fractions are withdrawn. During the recycling phase, no
feed solution or eluent is supplied to the sectional packing material beds and no
products are withdrawn. Such a sequential simulated moving bed method applied to the
recovery of betaine and sucrose from beet molasses is described in Finnish Patent
Application 882740 (U. S. Patent 5 127 957). Also the Applicants' copending Finnish
application 930321 (filing date January 26, 1993) relates to the fractionation of
molasses by a sequential simulated moving bed method.
[0023] The present invention relates to a sequential simulated moving bed method particularly
suitable for the fractionation of sulphite cooking liquor into at least three fractions.
In this method, the liquid flow is arranged in a system comprising at least two sectional
packing material beds, and the products are recovered during a multi-step sequence.
The sectional packing material bed may comprise one column; it is however also possible
to pack several successive sectional packing material beds in one column, depending
on the column structure. On the other hand, several successive columns may form one
or more loops.
[0024] A sequence comprises feeding, eluting and recycling phases. During the feeding phase,
sulphite cooking liquor is introduced into a sectional packing material bed and a
corresponding amount of product fraction is withdrawn at a point that may be located
either in the same sectional packing material bed as the feed point (in which case
the other sectional packing material beds in the system may be located for example
in the eluting or recycling step) or in a different sectional packing material bed
from that of the feed point, which bed is connected in series (possibly through other
sectional packing material beds) with the sectional packing material bed into which
the feed is effected. During the recycling phase, the liquid in the sectional packing
material beds with its dry solids profile is recycled in a loop comprising one, two
or several sectional packing material beds. In the eluting phase, eluent is introduced
into the packing material bed and a corresponding amount of product fraction(s) is
(are) withdrawn from the same or a downstream sectional packing material bed.
[0025] In the method of the invention, recycling is employed such that one, two, three or
even more discrete successive loops are formed in the recycling phase. For example,
the number of sectional packing material beds being three, these may form one loop
(in which case the method is called a single-phase method) or preferably two loops
(in which case the method is called a two-phase method), one of said loops comprising
one and the other two sectional packing material beds. When the system comprises several
successive discrete loops, each of these may be closed or open, that is, when the
liquid is recycled in one loop, eluent can be introduced into the other loop and a
product fraction can be withdrawn therefrom. During the feed and elution, the flow
through the packing material beds may be effected between the successive loops, the
flows conveying material from one loop to another. During the recycling phase, the
loop is closed and isolated from the other loops. Typically, one separate dry solids
profile is recycled in each of said discrete loops. Each sectional packing material
bed may form one discrete loop.
[0026] It has now been found that the sequential simulated moving bed method of the invention
is suitable for simultaneous recovery of xylose and lignosulphonates from sulphite
cooking liquor on an industrial scale in high yields and advantageous purity for further
processing or use. Furthermore, the salts, oligosaccharides such as xylobiose, and
other constituents in the sulphite cooking liquor which are harmful to the production
of xylose, can be advantageously removed from the xylose fraction by this method.
If a softwood sulphite cooking liquor were the raw material, the prevailing monosaccharide
would be mannose and a mannose-rich fraction would be obtained by the method.
[0027] If only a xylose fraction and residue fraction were separated in the method, the
lignosulphonates would be eluted with the organic and inorganic salts into the residue
fraction. However, the method of the invention yields a dry solids profile in which
lignosulphonates are concentrated in relation to salts, and they can be recovered
by suitably selecting the product withdrawal point.
[0028] The manner of realizing the method (single phase or multiphase) and the process parameters
employed are selected for example in accordance with the composition of the sulphite
cooking liquor employed as the raw material so as to reach an optimum result with
regard to the purity and yield of the product and the packing material capacity.
[0029] Preferably a strongly acid gel-type cation exchange resin (e.g. "Zerolit 225", "Finex"
or "Purolite") is employed as the packing material, and it preferably has the base
form of the cooking liquor. The ionic form of the packing material is equalized in
accordance with the base form of the cooking liquor in the course of the process if
the cooking liquor has not been subjected to any previous ion exchange.
[0030] A cooking liquor from the sulphite cooking of hardwood or any other pentosan-rich
biomass is employed as the feed solution. Prior to the separation, the solids contained
in the sulphite cooking liquor are removed therefrom by filtration, and the liquor
is fed into the separation process at a temperature of 20-95°C, more preferably 40-85°C,
most preferably 50-75°C.
[0031] Water at 20-95°C, more preferably 40-85°C, most preferably 50-75°C, is employed for
the elution.
[0032] The linear flow of liquid in the columns is 0.5-12 m
3/h/m
2, even 20 m
3/h/m
2, preferably 2-10 m
3/h/m
2.
[0033] The following examples illustrate the sequential simulated moving bed method of the
invention for fractionating sulphite cooking liquor. These examples shall not be regarded
as restricting the scope of the invention, but they are only examples of special embodiments
of the invention.
[0034] The dry solids contents indicated have been determined by the Karl Fischer method
unless otherwise stated. The lignosulphonate content has been determined by means
of UV absorbance measurement (absorptivity 14.25 l·g
-1·cm
-1).
[0035] In the examples, different types of filtered sulphite spent liquors were employed
as feed solutions: solution A had a low xylose content, solution B had a high xylose
content and solution C an average xylose content. The feed solutions were hardwood
sulphite spent liquors whose compositions were analyzed with a HPLC. All spent liquors
had calcium as a base. The analysis results are shown in Table 1, wherein the percentages
of the different constituents are given as per cent by weight on dry solids.
Table 1
Feed solution analyses |
|
Solution A |
Solution B |
Solution C |
Glucose, % |
1.3 |
+ |
1.7 |
Xylose, % |
11.5 |
21.5 |
19.6 |
Galactose+rhamnose, % |
1.0 |
1.4 |
1.5 |
Arabinose, % |
0.3 |
0.4 |
0.4 |
Mannose, % |
1.3 |
1.2 |
1.5 |
Monosaccharides tot.,% |
15.4 |
24.5 |
24.7 |
Oligosaccharides, % |
0.6 |
1.8 |
0.9 |
Lignosulphonates, % |
46.3 |
43.3 |
46.5 |
Others, % |
37.7 |
30.4 |
27.9 |
pH |
3.4 |
3.8 |
2.1 |
Conductivity, mS/cm |
9.8 |
3.6 |
11.0 |
Colour, ICUMSA Dry solids content, |
246000 |
71000 |
233000 |
% by weight |
47.3 |
54.7 |
33.6 |
Example 1
Single-phase separation method
[0036] The test apparatus included two columns connected in series, feed pumps, recycling
pumps, eluent water pumps, flow and pressure regulators, and inlet and product valves
for the different process streams. Each column comprised four sectional packing material
beds each having a height of about 1.39 m.
[0037] The columns were packed with a strongly acid cation exchange resin (Finex V 09 C™).
The resin had a polystyrene/divinylbenzene skeleton and was activated with sulphonic
acid groups; the mean bead size (in Na
+ form) was about 0.36 mm. The resin had a DVB content of 5.5%. Prior to the test the
resin had been regenerated to calcium form.
Test conditions: |
|
Diameter of columns |
0.2 m |
Total height of resin bed |
11.1 m |
Temperature |
70°C |
Flow rate |
130 and 170 l/h |
[0038] The feed solution was the above solution C.
[0039] Fractionation was performed by a four-step sequence. The duration of the sequence
was 110 minutes, and the sequence comprised the following steps:
Step 1: 60 1 of feed solution were introduced (feeding phase) into column 1 at a flow
rate 130 l/h, and a 60 1 residue fraction 1 was eluted from the downstream end of
the same column. Simultaneously water was supplied (eluting phase) to column 2 at
a flow rate 170 l/h, and a xylose fraction (45.0 l) and a residue fraction 2/1 (35
1) were eluted from the same column.
Step 2: 64.0 l were recycled (recycling phase) in the loop formed by the two columns,
at a rate 130 l/h.
Step 3: Water was introduced into column 1 at a rate 130 l/h and simultaneously a
residue fraction 2/2 (70 1) was eluted from column 2.
Step 4: 45 1 were recycled (recycling phase) in the loop formed by the two columns,
at a rate 130 l/h.
[0040] After the sequence was completed, the process control program was continued and it
returned to step 1. By repeating this sequence five to seven times the system was
equilibrated. The method was proceeded with in a state of equilibrium, and the progress
of the separation process was monitored with a density meter, a meter for optical
activity, and a conductivity meter, and the separation was controlled by a microprocessor
whereby precisely defined volumes and flow rates of feeds, recycled liquid and product
fractions were controlled employing quantity/volume measuring, valves and pumps.
[0041] In this method, four product fractions were withdrawn: a xylose fraction from column
2, one residue fraction from column 1, and two residue fractions from column 2. Analyses
of the product fractions withdrawn during one sequence after equalization are presented
in Table 2, where the percentages of the different constituents are given as per cent
by weight on dry solids.
[0042] The xylose yield in this fractionation was 75.6% calculated on the product fractions.

Example 2
Single-phase separation method
[0043] The test apparatus included three columns connected in series, feed pumps, recycling
pumps, eluent water pumps, flow and pressure regulators, and inlet and product valves
for the different process streams. Each column comprised one sectional packing material
bed.
[0044] The columns were packed with a strongly acid cation exchange resin (Finex V 09 C™).
The resin had a polystyrene/divinylbenzene skeleton and was activated with sulphonic
acid groups; the mean bead size (in Na
+ form) was about 0.39 mm. The resin had a DVB content of 5.5%. Prior to the test the
resin had been regenerated to calcium form.
Test conditions: |
|
Diameter of columns |
0.11 m |
Total height of resin bed |
12.0 m |
Temperature |
70°C |
Flow rate |
40 and 60 l/h |
[0045] The feed solution was the above solution A.
[0046] Fractionation was performed by a six-step sequence. The duration of the sequence
was 96 minutes, and the sequence comprised the following steps:
Step 1: 15.5 1 of feed solution were introduced (feeding phase) into column 1 at a
flow rate 40 l/h, and a 15.5 1 residue fraction 1 was eluted from the downstream end
of the same column. Simultaneously water was supplied (eluting phase) to column 2
at a flow rate 60 l/h, and a xylose fraction (8.0 1) and a residue fraction 3/1 (18.0
1) containing mainly salts were eluted from column 3.
Step 2: 16.0 1 were recycled (recycling phase) in the loop formed by all columns,
at a rate 40 l/h.
Step 3: Water was introduced into column 3 at a rate 40 l/h and simultaneously a lignosulphonate-rich
fraction (16 1) was eluted from column 2.
Step 4: 13.0 l were recycled (recycling phase) in the loop formed by all columns,
at a rate 40 l/h.
Step 5: Water was introduced into column 1 at a rate 40 l/h, and simultaneously a
residue fraction 3/2 (6.0 l) was eluted from column 3.
Step 6: 13.0 l were recycled (recycling step) in the loop formed by all columns, at
a rate 40 l/h.
[0047] After the sequence was completed, the process control program was continued and it
returned to step 1. By repeating this sequence five to seven times the system was
equilibrated. The method was proceeded with in a state of equilibrium, and the progress
of the separation process was monitored with a density meter, a meter for optical
activity, and a conductivity meter, and the separation was controlled by a microprocessor
whereby precisely defined volumes and flow rates of feeds, recycled liquid and product
fractions were controlled employing quantity/volume measuring, valves and pumps.
[0048] In this method, five product fractions were withdrawn: a xylose fraction from column
3, a residue fraction from column 1, two residue fractions from column 3 and a lignosulphonate-rich
fraction from column 2. Analyses of the product fractions withdrawn during one sequence
after equalization are presented in Table 3, where the percentages of the different
constituents are given as per cent by weight on dry solids.

[0049] The xylose yield in this fractionation was 87.4% calculated on the product fractions.
[0050] Figure 1 shows separation curves of column 2 for this fractionation. As can be seen
from Figure 1 and Table 3, the lignosulphonate-rich fraction is withdrawn from column
2. In the samples taken from the bottom of column 2 at the lignosulphonate peak at
intervals of four minutes, the lignosulphonate contents were 67.0, 79.2 and 75.0%
on dry solids. Figure 2 shows the separation curves of column 3 for this fractionation.
Example 3
[0051] The fractionation of Example 2 was repeated, but additionally the separation of lignosulphonates
having varying molar masses was analyzed.
[0052] Beginning from the start of the separation profile, samples were taken (four samples
per column) wherefrom the molar mass distribution of the lignosulphonates was analyzed.
The molar mass range was divided into five sections: more than 100 000 g/mol, 100
000 - 40 000 g/mol, 40 000-10 000 g/mol, 10 000-4 400 g/mol and less than 4 400 g/mol.
For column 2, Figure 1 indicates by numbers 1-4 the points at which the samples were
taken. The results obtained are shown in Table 4, which also shows for comparison
the corresponding analysis results of the feed solution.
[0053] Large-molecule lignosulphonates are concentrated in the lignosulphonate-rich fraction
(samples 2 and 3).

Example 4
Two-phase separation method
[0054] A chromatographic test apparatus comprising three columns, feed pumps, recycling
pumps, eluent water pumps, flow and pressure regulators, and inlet and product valves
for the different process streams was employed. The separation apparatus comprised
two loops, one of which was constituted by columns 1 and 2 in series and the other
by column 3.
[0055] The feed solution and the packing material of the columns were the same as in Example
2.
Test conditions: |
|
Diameter of columns |
0.11 m |
Total height of resin bed |
12.0 m |
Temperature |
75°C |
Flow rate |
25-75 l/h |
[0056] Fractionation was performed by a four-step sequence. The duration of the sequence
was 76 minutes, and the sequence comprised the following steps:
Step 1: 15.0 1 of feed solution were introduced (feeding phase) into column 1 at a
flow rate 30 l/h, and a 15.0 1 residue fraction 1 was eluted from the downstream end
of the same column. Simultaneously 18.0 1 of water were supplied (eluting phase) to
column 2 at a flow rate 35 l/h, and a residue fraction 3 (18.0 1) was eluted from
column 3.
Step 2: Recycling (recycling phase) in the loop formed by columns 1 and 2 (13.0 1;
50 l/h); simultaneously water was supplied to column 3 and a recycle fraction (3.0
1; 35 l/h) was eluted from column 3.
Step 3: Water was introduced into column 1, and simultaneously a lignosulphonate-rich
fraction (20.0 1; 75 l/h) was eluted from column 2, water was supplied to column 3
and a xylose fraction (18.0 1; 35 l/h was eluted from column 3.
Step 4: Recycling (recycling phase) in the loop formed by columns 1 and 2 (5.8 1;
75 l/h) and in the separate loop formed by column 3 (3.4 1; 25 l/h).
[0057] After the sequence was completed, the process control program was continued and it
returned to step 1. By repeating this sequence five to seven times the system was
equilibrated, whereafter the method was proceeded with in a state of equilibrium.
[0058] In this method, four product fractions were withdrawn: a residue fraction from columns
1 and 3, a lignosulphonate-rich fraction from column 2 and a xylose fraction from
column 3. The recycling fraction taken from column 3 was added to the feed solution.
Analyses of the product fractions withdrawn during one sequence after equalization
and of the recycling fraction are presented in Table 5, where the percentages of the
different constituents are given as per cent by weight on dry solids.
[0059] The xylose yield in this fractionation was 92.2%.

Example 5
Two-phase separation method
[0060] Fractionation was performed employing the separation apparatus described in Example
4, comprising two loops, and also the procedure of Example 4, except that the volume
parameters and flow rates of the feeds and withdrawn fractions were varied. These
variations were due to the higher xylose content of the feed solution.
[0061] The packing material of the columns was the same as in Examples 2-4. The feed solution
was solution B above.
Test conditions: |
|
Diameter of columns |
0.11 m |
Total height of resin bed |
12.0 m |
Temperature |
75°C |
Flow rate |
9-75 l/h |
[0062] Fractionation was performed by a four-step sequence. The duration of the sequence
was 84 minutes, and the sequence comprised the following steps:
Step 1: As step 1 in Example 4.
Step 2: Recycling (recycling phase) in the loop formed by columns 1 and 2 (13.0 1;
50 l/h); simultaneously water was supplied to column 3 and a recycle fraction (5.0
1; 35 l/h) was eluted from column 3.
Step 3: Water was introduced into column 1, and simultaneously a lignosulphonate-rich
fraction (20.0 1; 75 l/h) was eluted from column 2, water was supplied to column 3
and a xylose fraction (17.0 1; 35 l/h was eluted from column 3.
Step 4: Recycling (recycling phase) in the loop formed by columns 1 and 2 (5.8 1;
75 l/h) and in the separate loop formed by column 3 (2.2 1; 9 l/h).
[0063] This sequence was repeated five to seven times, whereafter the system was equilibrated
and the method was proceeded with in a state of equilibrium.
[0064] In this method, four product fractions were withdrawn: a residue fraction from columns
1 and 3, a lignosulphonate-rich fraction from column 2 and a xylose fraction from
column 3. The recycling fraction taken from column 3 was added to the feed solution.
[0065] Analyses of the product fractions and recycling fraction withdrawn during one sequence
after equalization are presented in Table 6. Percentages are given as per cent by
weight on dry solids.
[0066] The xylose yield in this fractionation was 90.7%.
[0067] The separation curves for this fractionation of column 2 are shown in Figure 3 and
of column 3 in Figure 4.
[0068] Table 6 shows that the oligosaccharide content in the xylose fraction is the smallest
of all withdrawn fractions and smaller than in the feed (solution B).

Example 6
Two-phase separation method
[0069] Fractionation was performed employing the separation apparatus described in Example
5, comprising two loops, and also the same packing material and feed solution as in
Example 5. Also the test conditions were the same as in Example 5 except for the flow
rates; no recycling fraction however was withdrawn.
[0070] The duration of the sequence was 84 minutes and the sequence comprised the following
four steps:
Step 1: 15.0 l of feed solution were introduced (feeding step) into column 1 at a
flow rate 37 l/h, and a 15.0 1 residue fraction 1 was eluted from the downstream end
of the same column. Simultaneously 18.5 1 of water were supplied (eluting step) to
column 2 at a flow rate 30 l/h, and a xylose fraction (18.5 1) was eluted from column
3.
Step 2: Recycling (recycling phase) in the loop formed by columns 1 and 2 (13.0 l;
50 l/h) and in the separate loop formed by column 3 (0.5 l; 9 l/h).
Step 3: Water was introduced into column 1, and simultaneously a residue fraction
2 (20.0 1; 75 l/h) was eluted from column 2, water was supplied to column 3 and a
residue fraction 3 (8 l; 35 l/h) was eluted from column 3.
Step 4: Recycling (recycling phase) in the loop formed by columns 1 and 2 (5.8 1;
75 l/h) and in the separate loop formed by column 3 (0.6 1; 9 l/h).
[0071] In this method, four product fractions were withdrawn: a residue fraction from each
column and a xylose fraction from column 3. Analyses of the product fractions and
recycling fraction withdrawn during one sequence after equalization are presented
in Table 7, where the percentages of the different constituents are given as per cent
by weight on dry solids. The dry solids content was determined by refractometric measurements.
[0072] The xylose yield in this fractionation was 89.2%.
